Circuit breaking section of a gas circuit breaker of the puffer type

ABSTRACT

A circuit breaking section of a gas circuit breaker of the puffer type comprising a nozzle made of an insulating material for directing an arc extinguishing gas pressurized by the movable cylinder and the fixed piston toward an arc produced between the fixed arc contact of the block shape and the movable hollow arc contact. The pressurized arc extinguishing gas is caused by the nozzle made of an insulating material to move in two directions or toward the orifice of the nozzle disposed on the downstream side thereof and the bore of the movable hollow arc contact. The nozzle is constructed such that its inner wall surface disposed on the upstream side of the nozzle and contiguous with the orifice forms an obtuse angle with the line of flow of gas directed toward the upstream side of the nozzle, so that more than half the volume of the pressurized arc extinguishing gas can be led toward the bore of the movable hollow arc contact.

United States Patent Tsubaki et al.

[451 Sept. 30, 1975 [75] Inventors: Tohru Tsubaki; Seizo Nakano;

Minoru Sato, all of Hitachi, Japan [73] Assignee: Hitachi, Ltd., Japan [22] Filed: Aug. 30, I974 [21] Appl. No.: 502,070

[30] Foreign Application Priority Data Aug. 27, 1974 Japan 49-26444 [52] US. Cl. 200/148 A; 200/150 G [51] Int. Cl. HOIH 33/70 [58] Field of Search 200/148 A, 150 G [56] References Cited UNITED STATES PATENTS 3,639,712 2/1972 Balmat et al ZOO/148 A 3,679,851 7/1972 Latour et a1. ZOO/148 A 3,786,215 l/1974 Mauthe ZOO/148 A 3,839,613 10/1974 Tsubaki et al. 200/148 A Primary E.\'aminerRobert S. Macon Attorney, Agent, or Firm-Craig & Antonelli [5 7 ABSTRACT A circuit breaking section of a gas circuit breaker of the pufi'er type comprising a nozzle made of an insulating material for directing an arc extinguishing gas pressurized by the movable cylinder and the fixed piston toward an are produced between the fixed arc contact of the block shape and the movable hollow arc contact. The pressurized arc extinguishing gas is caused by the nozzle made of an insulating material to move in two directions or toward the orifice of the nozzle disposed on the downstream side thereof and the bore of the movable hollow arc contact. The nozzle is constructed such that its inner wall surface disposed on the upstream side of the nozzle and contiguous with the orifice forms an obtuse angle with the line of flow of gas directed toward the upstream side of the nozzle, so that more than half the volume of the pressurized arc extinguishing gas can be led toward the bore of the movable hollow arc contact.

6 Claims, 1 Drawing Figure U.S. Patent Sept. 30,1975

CIRCUIT BREAKING'SECTION OF A GAS CIRCUIT BREAKER OF THE PUFFER TYPE BACKGROUND OF THE INVENTION This invention relates to circuit breaking sections of double flow gas circuit breakers of the puffer type, and more particularly it is concerned with improvements in or relating to the shape of a nozzle made of an insulating material for directing toward the arc an arc extinguishing gas pressurized by the puffer cylinder and puffer piston.

In recent years, there has been an increase in the demand for electric power which has made it necessary to transmit a current of high voltage and high value. With this tendency, the circuit breaking capacity required of circuit breakers is also on an increase. There is nowadays a demand for circuit breakers with a breaking current of 40 to 50 kilovolt amperes for use in a circuit of a voltage of over 100 kilovolts.

In gas circuit breakers of the puffer type, an are extinguishing gas under high pressure is produced by operating the puffer cylinder and blown against an are produced between the contacts to extinguish the same, thereby interrupting the current. SP gas or other insulating extinguishing medium is employed as an are extinguishing gas. I

In double flow gas circuit breakers of the puffer type of the prior art, the movable hollow arc contact juxtaposed against the fixed contact of the block shape and the movable main contact composed of a plurality of conducting pieces and surrounding the movable hollow arc contact are both positioned in a hollow space disposed on the upstream side of the nozzle made of an insulating material for blowing an arc extinguishing gas produced by the puffer piston and puffer cylinder against the arc. Because of this arrangement, the fixed contact and the movable contact (including the movable hollow arc contact) are brought into contact with each other in the interior of the nozzle. This makes it necessary to increase the volume (or diameter) of the portion of the nozzle disposed on the upstream side thereof, with an inevitable increase in the dead space within the nozzle. Thus, the arc extinguishing gas pressurized by the puffer cylinder and puffer piston is markedly lowered in pressure when it reaches the arc, thereby causing a reduction in the circuit breaking efficiency of the circuit breakers of this type.

The diameter of the orifice of the nozzle is selected such that it is larger than the diameter of the fixed contact to enable the fixed contact to pass through the orifice. This results in the major portion of the pressurized arc extinguishing gas moving through the orifice toward the downstream side of the nozzle, so that the volume of the pressurized arc extinguishing gas led into the bore of the movable hollow arc contact is greatly reduced. As a result, the movement of the arc along the inner wall of the movable hollow arc contact and cooling thereof are interfered with, thereby causing a reduction in the circuit breaking efficiency of the circuit breakers of this type.

With the orifice of the nozzle having a large diameter, a portion of the pressurized arc extinguishing gas is discharged throughthe orifice without contributing to the extinguishing of the arc. Because of this, it is necessary to produce more pressurized arc extinguishing gas than is necessary by the puffer cylinder and puffer piston. This in turn makes it necessary to increase the size of the puffer cylinder and puffer piston, thereby making it impossible to obtain an overall compact size in a circuit breaker operating device.

SUMMARY OF THE INVENTION An object of the invention is to provide a circuit breaking section of a double flow gas circuit breaker of the puffer type which exhibits a high circuit breaking performance.

Another object of the invention is to provide a circuit breaking section of a double flow gas circuit breaker of the puffer type in which substantially the total volume of an arc extinguishing gas pressurized by the puffer cylinder and puffer piston contributes to the extinguishing of the arc.

The outstanding characteristics of the invention are as follows. The main fixed contact is composed of a plurality of conductive pieces arranged in the form of a circle; the main movable contact juxtaposed against the main fixed contact is disposed along outer periphery of the nozzle of an insulating material for permitting an arc extinguishing gas pressurized by the puffer cylinder and puffer piston to move toward the arc; and the movable hollow arc contact alone is disposed in the hollow interior of the nozzle disposed on the upstream side thereof. The fixed arc contact of the block shape is disposed concentrically with the main fixed contact and juxtaposed against the movable hollow arc contact, so that the fixed arc contact can move through the orifice of the nozzle made of an insulating material and come into contact with the movable hollow arc contact in the hollow interior of the nozzle disposed on the upstream side thereof.

The nozzle has an inner wall which is shaped such that, when the circuit breaker is in a full open position in which the main fixed contact and the main movable contact are out of contact with each other, the resistance offered to the stream of a pressurized arc extinguishing gas supplied from a puffer chamber defined by the puffer cylinder and puffer piston and moving toward the bore of the movable hollow arc contact is smaller than the resistance offered to the stream of a pressurized arc extinguishing gas which moves toward the orifice of the nozzle from the puffer chamber. By this arrangement, more than half the total volume of the arc extinguishing gas flows into the bore of the movable hollow arc contact.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional view of the circuit breaking section of the double flow gas circuit breaker of the puffer type according to the invention, showing the circuit breaking section in a full open position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing is a sectional view of the circuit breaking section of the double flow gas circuit breaker of the puffer type comprising one embodiment of the invention, showing the circuit breaking section in its operative position in which it breaks the circuit. In the drawing, the main contacts comprise a main fixed contact 21 and a main movable contact 22. The main fixed contact 21 is composed of a plurality of conductive pieces arranged cylindrically and has spring means 23 mounted at its front end portion. A shield 24 for lowering the electric field intensity is provided on outer periphery of the spring means 23.

Provided in the central portion of the main fixed contact 21 is a fixed arc contact 25 of the block shape which is affixed to an immovable member (not shown) to which the main fixed contact 21 is also affixed. The fixed arc contact 25 has a forward end portion which is made of an arc resisting material.

On the other hand, puffer means comprising a puffer cylinder 26 and a puffer piston 27 is provided on the movable contact side. The main movable contact 22 serving concurrently as an insulator nozzle holding member to keep the base of an insulating nozzle 28 in place is connected through bolts 30 to a side wall 38 of the puffer cylinder 26 disposed on the contact side. The insulator nozzle 28 is formed on its downstream side with an orifice which has an inner diameter greater than the outer diameter of the fixed arc contact 25, and which steadily diverges in going outwardly. A hollow movable arc contact 31 is provided in the interior of the main movable contact 22 and has a forward end portion which is made of an arc resisting material as is the case with the forward end portion of the fixed arc contact 25.

The puffer cylinder 26 and puffer piston 27 define therebetween a puffer chamber 32 containing therein an arc extinguishing gas. Formed in the side wall 38 of the puffer cylinder 26 disposed on the contact side are gas supply ports 33 through which the arc extinguishing gas in the puffer chamber 32 moves and is blown against an are produced between the fixed arc contact 25 and the movable arc contact 31. Although only one gas supply port 33 is shown in the drawing, four gas supply ports 33 of the same sectional area are provided in this embodiment.

The insulator nozzle 28 is constructed such that its inner wall surface which is disposed on the upstream side thereof and contiguous with the orifice is planar, and that the planar inner wall surface of the nozzle 28 forms an angle 6 with the longitudinal center axis of the circuit breaker which is over 90. A flow control plate 34 made of an insulating material is provided on the outer side of the hollow movable arc contact 31 and constructed such that its main surface forms an angle a with the longitudinal center axis of the circuit breaker which is also over 90. The provision of the flow control plate 34 is conductive to reduced dead space in the interior of the nozzle and prevention of ignition to the extension of the main movable contact 22 or the bolts 30 by the arc. Since the movable arc contact 31 is used only for producing an arc when the circuit breaker breaks the circuit, and the current flows through the main contacts 21 and 22 when the circuit breaker is in a closed position in which it makes a circuit. Thus, the movable arc contact 31 is small in size because a current of high value flows therethrough for a very short time interval. Y

The insulator nozzle 28 is constructed such that the distance L between its planar inner surface disposed on the upstream side thereof and contiguous with the orifice and the side wall 38 of the puffer cylinder 26 is smaller than the radius R of the base of the insulator nozzle 28. This is conductive to reduced dead space in the interior of the nozzle 28 through which the are extinguishing gas moves after it has passed through the gas supply ports 33 and before it reaches an arc produced between the arc contacts 25 and 31. The nozzle 28 is constructed such that the planar inner surface thereof disposed on its upstream side and contiguous with the orifice and the main surface of the flow control plate 34 define therebetween a space of a sectional area which is disposed at right angles to the direction of flow of the pressurized arc extinguishing gas and substantially equal to the sum of sectional areas of the four gas supply ports 33. Thus, the dead space in the nozzle 28 is further reduced.

A tubular puffer cylinder shaft 36 supporting the movable hollow arc contact 31 is provided in the central portion of the puffer cylinder 26 and formed integrally therewith. The device described above is bodily disposed in a pressurized container (not shown) filled therein with SF gas and other arc extinguishing insulating gas.

The operation of the double flow gas circuit breaker of the puffer type constructed as aforementioned will now be described. When the circuit breaker is brought to a closed position in which it makes a circuit, the current passes through the main fixed contact 21, main movable contact 22 and puffer cylinder 27. In bringing the circuit breaker to an open position in which it breaks the circuit, the puffer cylinder shaft 36 is moved downwardly in the figure by a circuit breaker operating device (not shown). This moved downwardly the puffer cylinder 26, insulator nozzle 28, movable main contact 22 and movable arc contact 31 as a unit, thereby bringing the main contacts 21 and 22 out of contact with each other. When this is the case, the current passes though a path formed by the fixed arc contact 25, mov able arc contact 31 and puffer cylinder 26. Further downward movement of the puffer cylinder shaft 36 brings the arc contacts 25 and 31 out of contact with each other, thereby producing an are 35 therebetween.

On the other hand, the arc extinguishing gas contained in the puffer chamber 32 defined between the puffer cylinder 26 and puffer piston 27 is compressed and moves through the supply ports 33 to be blown against the arc 35. The are extinguishing gas blown against the arc 35 moves in two streams in two different directions or towards thebore of the movable hollow arc contact 31 and the orifice of the insulator nozzle 28. Thus, the gas is vented to the lower pressure portion of the container through the two outlets. The are 35 is extinguished as the pressurized arc extinguishing gas is blown thereagainst, thereby interrupting the flow of the current.

In the circuit breaking section of the circuit breaker according to the invention, the main contacts 21 and 22 are disposed outside the insulator nozzle 28 while the arc contacts 25 and 31 alone are disposed within the insulator nozzle 28. Thus, the orifice of the insulator nozzle 28 can have a diameter which is large enough to receive therein the fixed arc contact 25 of low current capacity. This keeps more arc extinguishing gas than is necessary for extinguishing the are from being discharged therethrough, so that the puffer chamber 32 can have a volume which is large enough to produce an essential minimum of pressurized are extinguishing gas.

The planar inner surface of the insulator nozzle 28 disposed on the upstream side thereof and contiguous with the orifice forms an angle 0 with the longitudinal center axis of the circuit breaker which is over The main surface of the flow control plate 34 forms an angle a with the longitudinal center axis of the circuit breaker which is also over 90. By virtue of these features, the pressurized arc extinguishing gas supplied through the gas supply ports 33 can be blown at right angles or at an obtuse angle against the arc 35 produced between the arc contacts and 31. As a result, the pressurized arc extinguishing gas can be introduced in a larger volume into the bore of the movable hollow arc contact 31 than into the orfifice of the nozzle 28,

. and the are 35 produced between the arc contacts 25 and 31 can be made to move along the inner wall of the movable hollow arc contact 31 in the same direction as the movement of the pressurized arc extinguishing gas, so that the arc can be readily cooled and positively extinguished.

Since the distance between the planar inner surface of the nozzle 28 disposed on the upstream side thereof and contiguous with the orifice and the side wall 38 of the puffer cylinder 26 disposed on the contact side is smaller than the radius of the base of the nozzle 28, the dead space in the path of movement of the arc extinguishing gas from the gas supply ports 33 to the arc 35 produced between the arc contacts 25 and 31 can be minimized, and a reduction in the pressure of the pressurized arc extinguishing gas can be prevented, thereby improving the circuit breaking efficiency of the circuit breaker. It should be understood in this connection that the distance between the planar inner surface of the nozzle 28 and the side wall of the puffer cylinder should be about Vs the radius of the base of the nozzle at a minimum, because the sectional area of the path of movement of the arc extinguishing gas will become too small and the resistance offered to the flow of gas will become too great if the distance is too small.

We claim:

1. A circuit breaking section of a gas circuit breaker of the puffer type comprising:

a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle,

b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact,

0. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact,

(1. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact,

e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall,

f. a fixed piston disposed in said movable cylinder for cooperation therewith,

g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod,

h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough,

i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out/of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and

j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated,

such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped that, when the circuit breaker is in a full open position in which the main fixed contact and the main movable contact are out of contact with each other, the resistance offered to a stream of gas moving from said plurality of gas supply ports toward the bore of said movable hollow arc contact is equal to or greater than the resistance offered to a stream of gas moving from said plurality of gas supply ports through the orifice of said nozzle made of an insulating material toward the downstream side thereof.

2. A circuit breaking section of a gas circuit breaker of the puffer type comprising:

a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle,

b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact,

c. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact,

d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact,

e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall,

f. a fixed piston disposed in said movable cylinder for cooperation therewith,

g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod;

h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough,

i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and

j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated,

such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped such that, when the circuit breaker is in a full open position in which the main fixed contact and the main movable contact are out of contact with each other, the volume of a pressurized gas moving from said plurality of gas supply ports toward the bore of said movable hollow arc Co tact is greater than or equal to the volume of a pressurized gas moving from said plurality of gas supply ports through the orifice of said nozzle made of an insulating material toward the downstream side thereof.

3. A circuit breaking section of a gas circuit breaker of the puffer type comprising:

a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle,

b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact,

c. a movable cylinder disposed in juxtaposed relation with said main fixed contact,

d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact,

e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall, I

f. a fixed piston disposed in said movable cylinder for cooperation therewith,

g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod,

h. a nozzle made of an insulating material disposed concentrically with said movable hollow contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough,

i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and

j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated,

such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped such that a stream of pressurized gas supplied through said plurality of gas supply ports and blown against an are produced between said fixed arc contact of the block shape and said movable conductive pieces arranged in the form of a circle,

b. a fixed are Contact of the block shape arranged concentrically in a hollow space of said main fixed contact,

c. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact,

d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact,

e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall,

f. a fixed piston disposed in said movable cylinder for cooperation therewith,

g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod,

h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough,

i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and V j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated,

such circuit breaking section being characterized in that said nozzle made of an insulating material is constructed such that the angle formed by its inner wall surface disposed on its upstream side and contiguous with said orifice with the line of flow of the gas directedtoward the upstream side of the nozzle is over 5. A circuit breaking section of a gas circuit breaker of the puffer type as claimed in claim 4 further comprising:

k. a flow control plate made of an insulating material disposed in said nozzle made of an insulating material and providing cover to said side wall while exposing a bore of said movable hollow arc contact and said plurality of gas supply ports.

6. A circuit breaking section of a gas circuit breaker of the puffer type as claimed in claim 5 wherein said flow control plate is constructed such that it has a main surface disposed on a side opposite said side wall, said main surface and the line of flow of the gas directed toward the upstream side of said nozzle made of an insulating material forming an angle which is over 90. 

1. A circuit breaking section of a gas circuit breaker of the puffer type comprising: a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle, b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact, c. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact, d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact, e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall, f. a fixed piston disposed in said movable cylinder for cooperation therewith, g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod, h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough, i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out/of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated, such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped that, when the circuit breaker is in a full open position in which the main fixed contact and the main movable contact are out of contact with each other, the resistance offered to a stream of gas moving from said plurality of gas supply ports toward the bore of said movable hollow arc contact is equal to or greater than the resistance offered to a stream of gas moving from said plurality of gas supply ports through the orifice of said nozzle made of an insulating material toward the downstream side thereof.
 2. A circuit breaking section of a gas circuit breaker of the puffer type comprising: a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle, b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact, c. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact, d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact, e. a hollow cylinder rod disposed concentrically with and extending through said moVable cylinder, said hollow cylinder rod being attached to said side wall, f. a fixed piston disposed in said movable cylinder for cooperation therewith, g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod; h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough, i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated, such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped such that, when the circuit breaker is in a full open position in which the main fixed contact and the main movable contact are out of contact with each other, the volume of a pressurized gas moving from said plurality of gas supply ports toward the bore of said movable hollow arc contact is greater than or equal to the volume of a pressurized gas moving from said plurality of gas supply ports through the orifice of said nozzle made of an insulating material toward the downstream side thereof.
 3. A circuit breaking section of a gas circuit breaker of the puffer type comprising: a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle, b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact, c. a movable cylinder disposed in juxtaposed relation with said main fixed contact, d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact, e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall, f. a fixed piston disposed in said movable cylinder for cooperation therewith, g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod, h. a nozzle made of an insulating material disposed concentrically with said movable hollow contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough, i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated, such circuit breaking section being characterized in that said nozzle made of an insulating material has an inner wall which is shaped such that a stream of pressurized gas supplied through said plurality of gas supply ports aNd blown against an arc produced between said fixed arc contact of the block shape and said movable hollow arc contact moves toward the upstream side of said nozzle made of an insulating material.
 4. A circuit breaking section of a gas circuit breaker of the puffer type comprising: a. a hollow main fixed contact including a plurality of conductive pieces arranged in the form of a circle, b. a fixed arc contact of the block shape arranged concentrically in a hollow space of said main fixed contact, c. a movable cylinder disposed in juxtaposed relation with said hollow main fixed contact, d. a side wall closing one end of said movable cylinder which is juxtaposed against said hollow main fixed contact, e. a hollow cylinder rod disposed concentrically with and extending through said movable cylinder, said hollow cylinder rod being attached to said side wall, f. a fixed piston disposed in said movable cylinder for cooperation therewith, g. a movable hollow arc contact disposed in juxtaposed relation with said fixed arc contact and supported in said hollow cylinder rod, h. a nozzle made of an insulating material disposed concentrically with said movable hollow arc contact and mounted on said side wall, said nozzle made of an insulating material being formed on its downstream side with an orifice of a diameter large enough to permit said fixed arc contact of the block shape to move therethrough, i. a main movable contact mounted on outer periphery of said nozzle made of an insulating material and disposed concentrically therewith so as to be brought into and out of sliding contact with said hollow main fixed contact, said main movable contact being electrically connected to said side wall, and j. a plurality of gas supply ports formed in said side wall for permitting a pressurized gas produced in a chamber defined in said movable cylinder between said side wall and said fixed piston to pass therethrough and move toward the downstream side of said nozzle made of an insulating material as said movable cylinder is operated, such circuit breaking section being characterized in that said nozzle made of an insulating material is constructed such that the angle formed by its inner wall surface disposed on its upstream side and contiguous with said orifice with the line of flow of the gas directed toward the upstream side of the nozzle is over 90*.
 5. A circuit breaking section of a gas circuit breaker of the puffer type as claimed in claim 4 further comprising: k. a flow control plate made of an insulating material disposed in said nozzle made of an insulating material and providing cover to said side wall while exposing a bore of said movable hollow arc contact and said plurality of gas supply ports.
 6. A circuit breaking section of a gas circuit breaker of the puffer type as claimed in claim 5 wherein said flow control plate is constructed such that it has a main surface disposed on a side opposite said side wall, said main surface and the line of flow of the gas directed toward the upstream side of said nozzle made of an insulating material forming an angle which is over 90*. 